A regular mattress and an RV mattress are almost the same thing however the difference mainly is in the size and how they're made to fit into the space.
RV Mattresses are usually a few inches shorter or narrower than a regular mattress of the same size you'd use in your home.
The RV Mattresses are usually a bit more flexible so they move around easily in the RV when bringing it into the RV.
If you do not like the RV Mattress then you can replace the RV Mattress with your favorite regular mattress although you might have to make a few adjustments to the area where the mattress fits in.
But you don't have to keep the RV Mattress in the RV if you don't like it and can change the Mattress out to one you like instead.